CSS Свойство justify-content space-around распределяет элементы не равномерно. Как исправить данную проблему?

.popup {
  position: fixed;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, 0.7);
  overflow-y: auto;
  overflow-x: hidden;
  opacity: 0;
  visibility: hidden;
}

.popup__body {
  min-height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 30px 10px;
}

.popup__container {
  background-color: #1f1f1f;
  color: #fff;
  font-weight: bold;
  font-size: 1.6rem;
  width: 100%;
  height: 300px;
  max-width: 600px;
  border-radius: 5px;
  overflow: hidden;
  margin-top: -1000px;
}

.popup__header {
  padding: 10px 30px;
  display: flex;
  align-items: center;
  font-size: 2.5rem;
  justify-content: space-between;
  margin-bottom: 20px;
  background-color: #3f3f3f;
  box-shadow: 0 2px 5px 2px #17181b;
}

.popup__close {
  -webkit-user-select: none;
  user-select: none;
  text-decoration: none;
}

.popup__close img {
  height: 30px;
  width: 30px;
}

.popup__content {
  padding: 10px 30px;
}

.popup__artist,
.popup__track {
  display: flex;
  margin-bottom: 25px;
  align-items: center;
}

.popup__artist p,
.popup__track p {
  flex-basis: 150px;
}

.popup__artist input,
.popup__track input {
  cursor: pointer;
  height: 35px;
  width: 65%;
  font-size: 1.5rem;
  font-weight: bold;
  padding: 0 10px;
  border-radius: 20px;
  background-color: #fff;
  border: 2px solid #fff;
  color: #000;
  text-overflow: ellipsis;
  transition: 0.4s;
}

.popup__artist input:hover,
.popup__track input:hover {
  background-color: transparent;
  color: #fff;
}

.popup__artist input:focus,
.popup__track input:focus {
  background-color: transparent;
  color: #fff;
  box-shadow: 0 4px 8px 4px #17181b;
}

.popup__artist input::placeholder,
.popup__track input::placeholder {
  letter-spacing: 1px;
}

.popup__btns {
  margin-top: 30px;
  display: flex;
  justify-content: space-around;
  padding-left: 10%;
}

.popup__upload {
  position: relative;
}

.popup__upload input {
  cursor: pointer;
  position: absolute;
  height: 100%;
  width: 100%;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  opacity: 0;
}

.popup__upload,
.popup__save {
  padding: 15px 25px;
  border: 1px solid #fff;
  min-width: 130px;
  background-color: transparent;
  font-size: 1.7rem;
  color: #fff;
  border-radius: 5px;
  font-weight: bold;
  text-align: center;
  -webkit-user-select: none;
  user-select: none;
  line-height: 100%;
  transition: 0.3s;
}

.popup__upload:hover,
.popup__save:hover {
  color: #000;
  background-color: #fff;
}

<div id="popup" class="popup">
  <div class="popup__body">
    <div class="popup__container">

      <div class="popup__header">
        <div class="popup__title">Add a new song</div>
        <a href="" class="popup__close">
          <img src="img/close.svg" alt="close">
        </a>
      </div>

      <form action="/upload" enctype="multipart/form-data" method="POST" name="fileupload" accept="audio/*" class="popup__content">

        <div class="popup__track">
          <p>Song name: </p>
          <input name="name" type="text">
        </div>

        <div class="popup__artist">
          <p>Artist: </p>
          <input name="artist" type="text">
        </div>

        <div class="popup__btns">

          <div class="popup__upload">
            Select File
            <input id="localFile" name="musicFile" multiple type="file">
          </div>

          <div>
            <button name="submitbutton" onclick="uploadFile(event)" class="popup__save" type="submit">Upload</button>
          </div>

          <div id="outputDiv"></div>

        </div>
      </form>
    </div>
  </div>
</div>