.ms-block-theme-minimal form {

}

.ms-block-theme-minimal form .ms-input,
.ms-block-theme-minimal form .ms-select,
.ms-block-theme-minimal form .ms-textarea {
    border: none !important;
    background: none;
    border-bottom: 1px solid !important;
    border-color: var(--ms-color-primary) !important;
    color: inherit !important;
    padding-left: 0;
    padding-right: 0;
}

.ms-block-theme-minimal form .ms-input:focus,
.ms-block-theme-minimal form .ms-select:focus,
.ms-block-theme-minimal form .ms-textarea:focus {
    border-color:  var(--ms-color-secondary) !important;
}